The invention relates to a brake shoe adjustment device for internally mounted shoe brakes, which is arranged between mutually neighboring ends of two brake shoes which are connected to each other via a tension spring. The brake shoes are held in position by mutually opposite spreading elements connected to each brake shoe end. One spreading element has a threaded shank which is screwed into an internal threaded bore of a worm wheel which in turn is mounted in a bearing bore of a receptacle. The worm wheel can be turned by means of a worm mounted in the receptacle. The worm wheel axis is normal to the axis of a brake drum. The worm can be turned by means of an adjusting tool which can be applied to it.
A brake shoe adjustment device of this general type is known from French Patent Specification No. 799,738. There, a cylindrical guide, with screw wheel toothing worked into the outer periphery in its central region, is mounted in a bore passing through the receptacle. The threaded bore for one spreading element is arranged centrally in the one face end of this guide and a bore for receiving a guide pin of the other spreading element is arranged centrally in its other face end.
The worm meshing with this toothing is mounted axially displaceably in the receptacle. Therefore, in order to be able to introduce the guide into the bore of the receptacle, its outside diameter is reduced (on its end piece having the pin bore) into the region of the toothing in such a way that the guide can be brought into engagement with the worm upon insertion into the bore of the receptacle. In order to secure the guide axially in the receptacle after its assembly, a stop and guide ring having essentially the bore diameter of the receptacle is introduced into the bore and pushed with radial pretension onto the guide end piece of reduced diameter. This stop and guide ring projects slightly beyond the cylindrical face end of the guide and is supported on the spreading element bearing the guide pin.
For adjusting the brake shoes, an adjusting tool is introduced to the inside shoe brake from the outside of the wheel via a wheel bore for a wheel bolt and must be applied to a worm wheel shank.
This known design requires a relatively large guide length, both for the guide forming the worm wheel and for the receptacle receiving and axially guiding the guide, which has to be fastened on the brake anchor plate. Such a design thus provides an adjustment device with a large dead weight.
Furthermore, this design requires an arrangement of two spreading elements which can be displaced axially by the guide in mutually opposite directions as well as an additional stop and guide ring, which further increases the weight, quite apart from the constructional outlay and the required axial securement of the worm in the receptacle.
It is therefore the object of the invention to provide a brake shoe adjustment device of the generic type which makes possible a reduction in: the number of individual parts, overall size and weight, and which is distinguished by a simple assembly of the worm wheel and the worm.
This object is achieved by having the worm wheel mounted with a laterally protruding bearing neck in the bearing bore of the receptacle forming the other spreading element. The receptacle has, adjacent to the periphery of the worm wheel, two bearing webs, which are arranged a distance from each other in the axial direction of the worm and which are each equipped with one bearing recess, which opens facing the worm wheel side, for bearing support of the worm.
The design comprises just one spreading element assigned to the receptacle. The threaded shank of the element is guided in the central threaded bore of the worm wheel, which protrudes with its bearing neck into the bearing bore of the receptacle and is supported by its one face on the receptacle.
The receptacle is supported on one of the two brake shoe ends and thus at that time also forms the other spreading element. This support of the receptacle on the brake shoe allows a stationary lashing of the latter to be dispensed with and permits the adjustment device to be merely clamped between the two brake shoes.
This means that the assembly of the worm gear is very simply accomplished by first placing the worm in the edge-open bearing recesses and subsequently bringing the worm wheel, preferably screwed in advance onto the threaded shank of the one spreading element, with the worm and with a bearing shank formed thereupon, into engagement with a bearing opening of the receptacle forming the other spreading element.
It is also advantageous if the adjusting device has a catch mechanism which utilizes the tension spring as the catching element and which engages with catch arrangements provided at the free face end of the worm upon its turning.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.